Note 6 - Investments in Joint Ventures - Condensed Balance Sheet of EXCOR and All Other Joint Ventures (Details) - USD ($)	12 Months Ended
	Aug. 31, 2016	Aug. 31, 2015
EXCOR [Member]
Current assets	$ 22,928,810	$ 22,620,323
Total assets	24,733,340	24,606,880
Current liabilities	3,485,231	3,360,142
Noncurrent liabilities
Joint ventures’ equity	21,248,109	21,246,738
Northern Technologies International Corporation’s share of joint ventures’ equity	10,624,056	11,571,361
Northern Technologies International Corporation's share of joint ventures’ undistributed earnings	10,593,151	11,540,456
Northern Technologies International Corporation's dividends received from joint ventures	4,364,700	2,440,200
All Other [Member]
Current assets	25,994,114	26,674,793
Total assets	27,673,686	28,247,058
Current liabilities	8,948,469	8,928,241
Noncurrent liabilities	100,783	1,215,139
Joint ventures’ equity	18,624,434	18,103,679
Northern Technologies International Corporation’s share of joint ventures’ equity	9,216,728	8,972,877
Northern Technologies International Corporation's share of joint ventures’ undistributed earnings	7,186,761	6,942,921
Northern Technologies International Corporation's dividends received from joint ventures	1,165,614	543,138
Current assets	48,922,924	49,295,116
Total assets	52,407,026	52,853,938
Current liabilities	12,433,700	12,288,383
Noncurrent liabilities	100,783	1,215,139
Joint ventures’ equity	39,872,543	39,350,417
Northern Technologies International Corporation’s share of joint ventures’ equity	19,840,774	20,544,238
Northern Technologies International Corporation's share of joint ventures’ undistributed earnings	17,779,912	18,483,377
Northern Technologies International Corporation's dividends received from joint ventures	$ 5,503,314	$ 2,983,338